1. Field of the Invention
The present invention relates to the field of liquid crystal display technology, and in particular to a GOA circuit structure.
2. The Related Arts
Liquid crystal display has many advantages of thin body, energy saving, no radiation, etc., which has been widely used. The liquid crystal display on the existing market is mostly backlight liquid crystal display, which comprises a liquid crystal panel and a backlight module. The working principle of the liquid crystal panel is to place liquid crystal molecules between two parallel glass substrates, and then apply driving voltage to the two parallel glass substrates to control the rotation orientation of the liquid crystal molecules, which refracts the light from the backlight module to generate image.
In the active matrix liquid crystal display, each pixel has a thin film transistor (TFT). The gate thereof is connected to the horizontal scanning line, the drain thereof is connected to the data line in the vertical direction, and the source thereof is connected to the pixel electrode. Applying enough voltage on the horizontal scanning line will turn on all TFTs on this line. At this time, the pixel electrodes on the horizontal scanning line will be connected with the data lines in the vertical direction, then write the display signal on the data lines into pixel, and control various liquid crystal transmittances to control the color. At present, the horizontal scanning lines of the active matrix liquid crystal display panel are mainly driven by the external IC of the panel. The external IC of the panel can control the each level horizontal scanning line to charge and discharge level by level. However, the gate driver on array (GOA) use the existing thin film transistor liquid crystal display array process to produce the gate row scanning driving signal circuit on the array substrate, which achieve the driving mode of progressively scanning the gate. Therefore, it can utilize the original process of the liquid crystal display panel to produce the driving circuit of the horizontal scanning line on the array substrate, which can replace the external IC to drive the horizontal scanning line. The GOA technology can reduce the bonding process of the external IC, have chance to improve the capacity and decrease the product cost, and make the liquid crystal display panel more suitable for the production of narrow border or borderless display products.
The existing GOA circuit usually comprises multiple GOA units cascaded with each other. Each level GOA unit correspondingly drives one-level horizontal scanning line. GOA unit mainly comprises a pull-up part, a pull-up control part, a transfer part, a key pull-down part, a pull-down holding part, and a boast capacitor used to raise potential. The pull-up part is mainly used to output clock signal into gate signal; the pull-up control part is mainly used to control the turning-on time of the pull-up part, which is usually connected with the transfer signal or the gate signal transferred from the preceding level GOA circuit; the pull-down part is used to pull-down the gate to low potential at a first time, that is, close the gate signal; the pull-down holding part is used to hold the gate outputting signal and the gate signal (usually called Q point) of the pull-up part in the off state (negative potential), which usually has two pull-down holding module working alternately; the boast capacitor is used to twice raise the Q point, which is beneficial to the G(N) output of the pull-up part.
In the existing GOA circuit structure, basically, the above sections are placed in the same level GOA unit circuit, especially in amorphous silicon GOA circuit, the two important pull-down holding circuit are working alternately in the same level GOA circuit, as shown in FIG. 1, which is a schematic view illustrating the GOA circuit structure according to the existing technology. The metal wires used to transfer DC low voltage VSS, four high frequency clock signals CK1˜CK4 are placed at the peripheral of each level GOA circuit. Each level GOA unit respectively has first pull-down holding circuit and second pull-down holding circuit. The first pull-down holding circuit and the second pull-down holding circuit are respectively connected between Q(N) and G(N), which is used to alternately hold the Q(N) and the G(N) in the off state. The N-th level GOA unit circuit respectively receive VSS and one CK signal of CK1˜CK4 to generate G(N) signal. STV signal is a starting signal of the GOA circuit. Therefore, the STV signal is used to start the first level and the second level GOA unit circuit, and the starting signal of the latter N-th level GOA circuit is generated from the ST(N−2) signal of the transfer part of the former (N−2)-th level circuit. In this way, it can gradually turn on the GOA driving circuit and achieve the scanning drive. The connecting method within each GOA unit circuits shown in FIG. 1 can ensure that the GOA signal can be gradually transferred, which allows each level horizontal scanning line be gradually charged and discharged.
This structure has the following disadvantages:    1. The first and the second pull-down holding circuit work alternately, namely, the working time and the rest time are half-half, but the stress recovery time is still shorter for TFT, so that the failure of the pull-down holding circuit is more serious than the other;    2. The pull-down holding circuit and the Q point of the adjacent level GOA units have no interaction, so the actual effect of the circuit is inefficient, which is because the gate signal is only turned on for a moment, and the other long time is in close state, the pull-down time and the Q point waveform of the adjacent GOA units are basically the same;    3. The pull-down holding part is generally using a high-frequency control signals, which will increase the power consumption of the circuit; the two low-frequency control signals are also used, but it will also increase the stress effect of TFT.